TOKYO — Last year’s nuclear crisis at Japan’s Fukushima Daiichi plant was a “profoundly man-made disaster,” the result of poor earthquake-safety planning and faulty post-tsunami communication, a report from an independent parliamentary panel said Thursday.

The sharp criticism of the Japanese government and the nuclear operator Tokyo Electric Power Co. (Tepco) provided an alternative narrative to an earlier investigation by Tepco, whose in-house panel concluded that the disaster was unforeseeable, spurred by a “giant tsunami beyond our imagination.”

In contrast, the report released Thursday suggested that the 9.0-magnitude earthquake that triggered the tsunami may have caused critical damage that led to the series of meltdowns. It argued that the nuclear power plants should have been made more quake-proof, and blamed lax safety measures on what it called the country’s powerful and “collusive” decision-makers and on a conformist culture that allowed them to operate with little scrutiny.

The nuclear bloc, while reassuring the nation about its safe atomic plants, ignored safeguards that would have helped strengthen the Fukushima facility against a massive but foreseeable earthquake, the 641-page report said.

In a blistering assessment, the authors described how regulators and nuclear operators went to painstaking lengths to ignore safety risks at the plant or cover them up. It accused Tepco and government officials of slow and faulty communication after the disaster, which, the report said, hampered the emergency response.

Regulators and nuclear operators disregarded earlier warnings from outside watchdog groups that earthquakes posed a significant safety risk to the nuclear plants, an English summary of the report said. In the process, they “effectively betrayed the nation’s right to be safe from nuclear accidents.”

“What must be admitted — very painfully — is that this was a disaster ‘Made in Japan,’ ” investigation chairman Kiyoshi Kurokawa wrote in the introduction to the report. “Its fundamental causes are to be found in the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to ‘sticking with the program’; our groupism; and our insularity.”

Before the accident, nuclear power supplied almost one-third of Japan’s energy. But many plants sit near seismic faults, and the parliamentary panel’s suggestion about earthquake damage could increase already fierce public opposition to restarting the nuclear reactors. It also may force Japanese utilities to perform pricey earthquake retro-fitting.

The triple meltdown at the Fukushima plant spread significant radiation across 700 square miles of land and forced more than 100,000 people to evacuate. Facing growing public opposition to atomic energy, Japan shuttered all of its nuclear plants after the disaster. Only on Thursday did the first reactor — at the Ohi plant in western Japan — resume generation.

The report raised the possibility that the earthquake damaged critical safety equipment. Tepco, the report said, was quick to blame the tsunami in its own statements, presumably as a way to “avoid responsibility” by attributing the meltdowns to the unexpected tsunami, rather than the “more foreseeable earthquake.”

Japan needs to overhaul its nuclear regulation system, the report said, creating an independent watchdog: Previously, the safety agency was a part of the same government ministry that promoted nuclear power. The report said the Nuclear and Industrial Safety Agency (NISA) did not press Tepco to prepare for a so-called full station blackout — the loss of main and backup power — because the “probability was small.” NISA instead asked Tepco to explain why new prevention measures would not be necessary.

The report released Thursday describes a post-tsunami breakdown in communication and cooperation between those who operated the Fukushima plant and those who handled Japan’s nuclear safety.

The prime minister’s office waited too long to declare a state of emergency. Tepco’s disaster-response manuals were out of date and missing key diagrams. The company was too slow to relay information to the government.

Then-Prime Minister Naoto Kan traveled to the plant mid-meltdown and “diverted the attention and time of the on-site operational staff and confused the line of command,” the report said.

“Had the head office of Tepco actively communicated the on-site situation from the start, and explained the severity of the situation to the other parties,” the report said, “there is a possibility that the distrust — and the confusion in the chain of command that followed — could have been prevented.”

The 10-member commission compiled its report based on more than 1,000 interviews and 900 hours of hearings.

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